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The actor's father showed the diary to producers of 2012 German docu-series, "Too Young to Die"

Heath Ledger posthumously won an Oscar for his role as sociopathic "Dark Knight" villain, The Joker, and a new glimpse inside the personal diary he created for the performance is another reminder of his dedication to the character.

The journal was featured in a German docu-series, "Too Young to Die," during which Ledger's father, Kim, flips through its pages to demonstrate his son's method of immersing himself in a character.

Ledger alluded to the diary in a 2007 interview with Empire magazine in which he explained that he resorted to solitary confinement in order to create what would become his most iconic performance.

"I sat around in a hotel room in London for about a month, locked myself away, formed a little diary and experimented with voices — it was important to try to find a somewhat iconic voice and laugh," the actor told the British magazine a few months before his death.

In the clip, Ledger's father points to a hand-written version of the monologue his son gives to Harvey Dent (Aaron Eckhart) while dressed as a female nurse in the hospital scene.

"The hospital scene is interesting because when he was a kid, his sister Kate liked to dress him up as a nurse," Kim says. "He was really funny like that."

Not so funny, however, are two ominous words written on the back of a page with a picture of Ledger's Joker make-up test.

"Bye, Bye."

Take a look inside the actor's mind, below:

Here is a translation of the German voiceover:

"This is the Joker's diary. In order to inhabit his character, he [Heath] locked himself up in a hotel room for weeks. He would do that. He liked to dive into his characters, but this time he really took it up a notch. The hospital scene is interesting because when he was a kid, his sister Kate liked to dress him up as a nurse. He was really funny like that. He also was in the movie. This is a makeup test, which was done eight months before. Before the end of the shooting he wrote 'bye-bye' on the back of the page. It was hard to see this."